With the exceptions listed below, clauses are executed in the loop body
in the order in which they appear in the source. Execution is repeated
until a clause
terminates the loop or until a Common Lisp return,
go, or throw form is encountered. The following actions are
exceptions to the linear order of execution:

All variables are initialized first, regardless of where the establishing
clauses appear in the source. The order of initialization follows the
order of these clauses.

The code for any initially clauses is collected
into one progn in the order in which the clauses appear in
the source. The collected code is executed once in the loop prologue
after any implicit variable initializations.

The code for any finally clauses is collected
into one progn in the order in which the clauses appear in
the source. The collected code is executed once in the loop epilogue
before any implicit values from the accumulation clauses are returned.
Explicit returns anywhere in the source, however, will exit the loop
without executing the epilogue code.

A with clause introduces a variable binding and an optional
initial value. The initial values are calculated in the order in
which the with clauses occur.

Iteration control clauses implicitly perform the following actions:

initializing variables

stepping variables, generally between each execution of the loop body

performing termination tests, generally just before the execution of the
loop body